Contact structure and contact liner process

ABSTRACT

A contact structure and a method of forming thereof for semiconductor devices or assemblies are described. The method provides process steps to create a contact structure encompassed by a sacrificial contact medium having an opening therein that is lined with a conductive spacer liner that effectively prevents the contact structure from being damaged during removal of the surrounding sacrificial contact medium material. The sacrificial contact medium is then replaced with a non-boron doped dielectric material.

FIELD OF THE INVENTION

This invention relates to semiconductor fabrication processing and, moreparticularly, to a method for forming a contact structure liner forsemiconductor devices, such as static random access memories (SRAMS) ordynamic random access memories (DRAMs).

BACKGROUND OF THE INVENTION

The continuing trend of scaling down integrated circuits has motivatedthe semiconductor industry to consider new techniques for fabricatingprecise components at sub- micron levels. One important area insemiconductor fabrication is forming the interconnecting structurewithin the integrated circuit and particularly connections betweenvarious levels of metal layers.

As is the case for most semiconductor integrated circuitry, circuitdensity is continuing to increase at a fairly constant rate. Insemiconductor devices it may be advantageous to build contact plugs forinterlayer connections having high aspect ratio structures, as circuitdensity will be enhanced. In that light, it becomes critical that thecontact structure, particularly were the structure makes physicalcontact to an underlying conductor, is not damaged during processing.

Forming contact plugs to regions in a semiconductor device are wellknown. For example, U.S. Pat. No. 6,518,626 describes a method to form aself-aligned contact to a source/drain region of a transistor. Thecontact is fabricated between transistor gate stacks having sidewallspacers, often formed of an oxide or nitride. The process includesforming an insulating layer, for example an oxide such as BPSG, over thegate stacks and etching through the insulating layer. The sidewallspacers on the gate stack protect the gate stack and allow for lateralmargin during the etching process. The etching process, however, doesremove some of the sidewall spacer. As the thickness of the spacerdecreases with advances in semiconductor designs, removal of a portionof the spacer can create short circuits between the transistor gatestack and the conductive contact plug.

The present invention describes a contact structure and a method to formthe contact structure that addresses the above challenges.

SUMMARY OF THE INVENTION

Exemplary implementations of the present invention include a contactstructure and a method of forming thereof for semiconductor devices orassemblies. The method provides process steps to create a contactstructure encompassed by a sacrificial contact medium having an openingtherein that is lined with a protective spacer liner that effectivelyprevents the contact structure from being damaged during removal of thesurrounding sacrificial contact medium material. The sacrificial contactmedium is then replaced with a non-boron doped dielectric material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a semiconductor substrate sectiondepicting a sacrificial self-aligned contact medium on a substrateassembly.

FIG. 2 is a subsequent cross-sectional view taken from FIG. 1 followingthe formation of a sacrificial liner material over the sacrificialself-aligned contact medium and the exposed portion of the substrateassembly.

FIG. 3 is a subsequent cross-sectional view taken from FIG. 2 followingthe removal of the sacrificial liner material to leave a liner materialportion on the vertical surfaces of the sacrificial self-alignmentcontact medium.

FIG. 4 is a cross-sectional view taken from FIG. 5 following theformation of a barrier material, an adhesion material, and a conductiveplug, all of which are planarized.

FIG. 5 is a cross-sectional view taken from FIG. 4 following the removalof the sacrificial self-alignment contact medium.

FIG. 6 is a cross-sectional view taken from FIG. 5 following theformation of a sacrificial self-alignment contact medium replacementmaterial.

FIG. 7 is cross-sectional view showing a completed interconnectstructure between transistor source/drain regions and a self-alignedcontact plug depicting an embodiment of the present invention.

FIG. 8 is a simplified block diagram of a semiconductor systemcomprising a processor and memory device to which the present inventionmay be applied.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary implementations of the present invention are directed tocontact structures and processes for forming a self-aligned contact plughaving protective liners and being encompassed by a non-boron containingdielectric for fabrication of semiconductor assemblies, such as asemiconductor device as depicted in the embodiments of FIGS. 1-8. Thepresent invention is described herein with reference to a contact madeto an active device, such as a field effect transistor, but can beimplemented in stand alone, or discrete contacts.

In the following description, the terms “wafer” and “substrate” are tobe understood as a semiconductor-based material including silicon,silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology,doped and undoped semiconductors, epitaxial layers of silicon supportedby a base semiconductor foundation, and other semiconductor structures.Furthermore, when reference is made to a “wafer” or “substrate” in thefollowing description, previous process steps may have been utilized toform regions or junctions in or over the base semiconductor structure orfoundation. In addition, the semiconductor need not be silicon-based,but could be based on silicon-germanium, silicon-on-insulator,silicon-on-saphire, germanium, or gallium arsenide, among others.

Referring now to FIG. 1, substrate 10, such as a semiconductor assembly,is prepared for processing steps of an embodiment of the presentembodiment. Residing in substrate 10 is a conductive material or asemiconductive region 13, such as a metal layer, a source/drain of atransistor implanted into a conductively doped silicon wafer or a metalsilicide, such as titanium silicide (TiSi₂).

A sacrificial self-aligned contact medium 11, such asborophosphosilicate glass (BPSG) is placed on substrate 10 andsubsequently patterned to provide a defined contact opening location(via) 12, which exposes conductor 13 residing in a portion of substrate10. It is preferred that sacrificial contact medium 11 be an insulativematerial rather than a conductive material so that a subsequent removalof the sacrificial contact medium 11 surrounding a subsequently formedadjacent conductive material is easily accomplished by methods known tothose skilled in the art in that the sacrificial (insulative) material11 is removed without removing the adjacent conductive material.

Referring now to FIG. 2, a self-aligned contact liner material 20, forexample a metal material, and more particularly a preferred metal,namely tungsten, is formed to cover sacrificial self-aligned contactmedium 11 (conforming to both the horizontal and vertical components ofmedium 11) and the exposed portion of substrate 10.

Referring now to FIG. 3, the liner material 20 is selectively removed bymethods known to one skilled in the art, such that a vertical componentof the liner material remains to form conductive vertical liner spacer30 residing on the vertical sidewalls of medium 11, while the horizontalcomponents are removed to expose underlying conductor 13. Conductivevertical liner spacer 30 will also serve as barrier layer to limit theamount of out-diffusion of heavy conductive atoms, such as boron, fromneighboring doped insulation material subsequently formed as depicted inFIG. 6. Ultimately, the doped insulation material formed in the processsteps depicted in FIG. 6 will replace sacrificial contact medium 11.

Referring now to FIG. 4, a second barrier layer 40, such as titanium, anadhesion layer 41, such as titanium nitride, and conductive plugmaterial 42, such as tungsten, are sequentially formed over medium 11and into via 12. The barrier layer 40 can be a metal layer that willprevent conductive atoms from diffusing through it. The type of metalused for barrier layer 40 will determine the type of adhesion materialselected for adhesion layer 41 so that strong atomic bonding occursbetween the second barrier layer and the adhesion layer as well asbetween the adhesion layer and the conductive plug materials. Forexample, if titanium is selected for second barrier layer 40, then usingtitanium nitride as the adhesion layer will provide good adhesionbetween titanium layer 40 and a conductive plug material 42, liketungsten.

Layers 40, 41 and 42 are then subjected to a planarization process knownto those skilled in the art, such as chemical mechanical planarization.After the planarization of layers 40, 41 and 42, a self-aligned contactis formed comprising conductive vertical liner spacer 30 (also serves asa diffusion barrier layer), barrier layer 40, adhesion layer 41 andconductive plug material 42. Barrier layer 40 will further limit theamount of out-diffusion of conductive atoms from a neighboring dopedinsulation material formed during a given fabrication process.

Though FIG. 4 depicts three layers to form a self-aligned contact, anynumber of layers may be formed as required in a given process to form acontact. For example, although described in the exemplary embodiment ofthe present invention, barrier layer 40 and adhesion layer 41 areoptional materials and need not be present as conductive vertical linerspacer 30 and conductive plug material 42 will suffice as the conductorif so desired, without departing from the intent of the presentinvention.

Referring now to FIG. 5, medium 11 is removed by such methods aswet/dry/vapor etch techniques, or any combinations thereof, know tothose skilled in the art. The removal of medium 11 leaves vertical linerspacer 30 intact and residing next to barrier layer 40 to form astructure 50 comprising a contact structure 51 having protectivevertical liner spacer 30. In addition to functioning as an out-diffusionbarrier, the presence of the protective spacer 30 also becomessignificant during the removal of medium 11 as protective spacer 30prevents any removal or damage to the underlying conductor 13, shouldthere be any process margin variations associated with smaller devicegeometries being processed with the current fabrication processes.

Referring now to FIG. 6, a self-aligned contact medium replacementmaterial 60 is formed over the semiconductor assembly such thatreplacement material 60 covers substrate 10 and structure 50. Forexample, replacement material 60 may comprise such materials asphosphosilicate glass (PSG) or other non-boron containing dielectrics,as boron atoms (such as B10) are known to diffuse into neighboringmaterials and degrade the electrical characteristics of active devices,such as field effect transistors (FETs). Also, as mentioned previously,it is desired that a barrier layer be in place to limit the diffusion ofheavy conductive atoms, such as boron, should a boron containingdielectric be used. Finally, replacement material 60 may then beplanarized in preparation for subsequent process steps used to completefabrication of a given semiconductor assembly or device.

FIG. 7 depicts an example of a device utilizing the process steps of thepresent invention. As shown in FIG. 7, processing steps, known by oneskilled in the art, are used to form field effect transistors (FETs) ina silicon substrate 70. The FETs comprise source/drain regions 71 thatspan between insulated transistor gate electrodes 72. Insulatedtransistor gate electrodes 72 are typically made up of a transistor gateoxide and conductive layers, such as polysilicon and silicide,respectively, which are isolated by transistor gate cap insulator, madefrom dielectric materials such as nitride. Insulation material 73 coversthe insulated transistor gate electrodes and contact 74 is formedtherein that connects between to source/drain region 71 and an overlyingconductive material 75. Conductive material 75 represents conductor 13residing in substrate 10 seen in FIG. 1 and is at the point theprocessing steps of the present invention are utilized. As described inthe process steps of FIGS. 1-6, protective spacer liner 76 is formedinto a contact via (or opening), followed by the formation of barrierlayer 77, adhesion layer 78 and conductive plug material 79 to form acontact structure. Replacement material 80 insulates the contactstructure and an interconnect 81 is formed to connect to the contactstructure.

FIG. 7 represents only one example of a type of semiconductor device orassembly the process steps of the present invention may be used for.Though the embodiment of the present invention depicts a deviceutilizing self-aligned contact technology, the present invention maysuccessfully be used on other technologies, such as any contact,damascene or trench processes know to those skilled in the art.

The self-aligned contact structures and the formation thereof, asdescribed above for development in semiconductor devices, may be appliedto a semiconductor system, such as the one depicted in FIG. 8. FIG. 8represents a general block diagram of a semiconductor system, thegeneral operation of which is known to one skilled in the art, thesemiconductor system comprising a processor 82 and a memory device 83showing the basic sections of a memory integrated circuit, such as rowand column address buffers, 84 and 85, row and column decoders, 86 and87, sense amplifiers 88, memory array 89 and data input/output 90, whichare manipulated by control/timing signals from the processor throughcontrol 91.

It is to be understood that although the present invention has beendescribed with reference to a preferred embodiment, variousmodifications, known to those skilled in the art, such as utilizing thedisclosed methods to form a protect liner for contacts in anysemiconductor device or semiconductor assembly, may be made to theprocess steps presented herein without departing from the invention asrecited in the several claims appended hereto.

1. A semiconductor assembly having a contact structure comprising: acontact structure encompassing material having an opening therein thatgives access to an underlying conductor; a conductive vertical linerspacer that resides on sidewalls of the opening in the contact structureencompassing material; and a conductive plug material residing withinvertical components of the conductive vertical liner spacer and coveringa horizontal component of the underlying conductor.
 2. The semiconductorassembly of claim 1, wherein the conductive plug material comprisestungsten.
 3. The semiconductor assembly of claim 1, wherein theconductive vertical liner spacer comprises tungsten.
 4. Thesemiconductor assembly of claim 1, wherein the contact structureencompassing material comprises a non-boron containing dielectric. 5.The semiconductor assembly of claim 4, wherein the non-boron containingdielectric is phosphosilicate glass (PSG).
 6. A semiconductor assemblyhaving a contact structure comprising: a contact structure encompassingmaterial having an opening therein that gives access to an underlyingconductor; a conductive vertical liner spacer that resides on sidewallsof an opening in the contact structure encompassing material; a barrierlayer lining the conductive vertical liner spacer and a horizontalcomponent of the underlying conductor; an adhesion layer lining thebarrier layer; and a conductive plug material residing within verticalcomponents and covering a horizontal component of the adhesion layer. 7.The semiconductor assembly of claim 6, wherein the conductive plugmaterial is tungsten.
 8. The semiconductor assembly of claim 6, whereinthe adhesion layer is titanium nitride.
 9. The semiconductor assembly ofclaim 6, wherein the barrier layer is titanium.
 10. The semiconductorassembly of claim 6, wherein the conductive vertical liner spacercomprises tungsten.
 11. The semiconductor assembly of claim 6, whereinthe contact structure encompassing material comprises a non-boroncontaining dielectric.
 12. The semiconductor assembly of claim 11,wherein the non-boron containing dielectric is phosphosilicate glass(PSG).
 13. A contact structure for a semiconductor assembly comprising:a contact structure encompassing non-boron containing dielectricmaterial; a vertical tungsten spacer that resides on sidewalls of anopening in the contact structure encompassing non-boron containingdielectric material; a titanium barrier layer lining the verticaltungsten spacer and a horizontal component of an underlying conductor; atitanium nitride adhesion layer lining the titanium barrier layer; and aconductive tungsten plug material residing within vertical componentsand covering a horizontal component of the titanium nitride adhesionlayer.
 14. The semiconductor assembly of claim 13, wherein the non-boroncontaining dielectric is phosphosilicate glass (PSG).
 15. A method of aforming a semiconductor assembly having a contact structure comprising:forming a sacrificial contact structure encompassing material having anopening therein that exposes an underlying conductor; forming aconductive vertical liner spacer on sidewalls of the opening in thesacrificial contact structure encompassing material; forming aconductive plug material within vertical confines of the conductivevertical liner spacer and covering a horizontal component of theunderlying conductor; removing the sacrificial contact structureencompassing material; and forming a final contact structureencompassing material.
 16. The method of claim 15, wherein theconductive plug material is tungsten.
 17. The method of claim 15,wherein the conductive vertical liner spacer comprises tungsten.
 18. Themethod of claim 15, wherein the contact structure encompassing materialcomprises a non-boron containing dielectric.
 19. The method of claim 18,wherein the non-boron containing dielectric is phosphosilicate glass(PSG).
 20. A method of a forming a semiconductor assembly having contactstructure comprising: forming a sacrificial contact structureencompassing material having an opening therein that exposes anunderlying conductor; forming a conductive vertical liner spacer onsidewalls of the opening in the sacrificial contact structureencompassing material; forming a barrier layer lining the conductivevertical liner spacer and a horizontal component of the underlyingconductor; forming an adhesion layer conformably lining the barrierlayer; forming a conductive plug material within vertical components theadhesion layer and covering a horizontal component of the adhesionlayer; removing the sacrificial contact structure encompassing material;and forming a final contact structure encompassing material.
 21. Themethod of claim 20, wherein the conductive plug material is tungsten.22. The method of claim 20, wherein the adhesion layer is titaniumnitride.
 23. The method of claim 20, wherein the barrier layer istitanium.
 24. The method of claim 20, wherein the conductive verticalliner spacer comprises tungsten.
 25. The method of claim 20, wherein thecontact structure encompassing material comprises a non-boron containingdielectric.
 26. The method of claim 25, wherein the non-boron containingdielectric is phosphosilicate glass (PSG).
 27. A method of forming acontact structure for a semiconductor assembly comprising: forming asacrificial borophophosilicate glass material having an opening thereinthat exposes an underlying conductor; forming a vertical tungsten spaceron sidewalls of the opening in the sacrificial borophophosilicate glassmaterial; forming a titanium layer lining the vertical tungsten spacerand a horizontal component of the underlying conductor; forming atitanium nitride layer conformably lining the titanium layer; forming atungsten plug material within vertical components the titanium nitridelayer and covering a horizontal component of the titanium nitride layer;removing the sacrificial borophophosilicate glass material; and forminga non-boron containing dielectric material that encompasses the contactstructure.
 28. The method of claim 27, wherein the non-boron containingdielectric material is phosphosilicate glass (PSG).